Problems of membrane function are now recognized to be of central importance for medicine, as well as for cell biology. Areas of great clinical concern, such as the mechanism of action of insulin and other hormones, the functions of the kidney in maintaining homeostasis, and the maintenance of the integrity of the erythrocyte, are all intimately related to membrane function. The proposed work is aimed at a fundamental aspect of membrane biogenesis -- the biosynthesis and function of the phospholipid components. It includes studies of living cells of Escherichia coli by isotope tracer methods, and of enzymes in cell-free extracts. The regulation of the biosynthesis of membrane components will also be studied in experiments that combine genetic and enzymological approaches.